This invention relates generally to a system of operating an automatic plotting device having different marking instruments for drawing characters and images onto a sheet. Specifically, this invention relates to a system of operating an automatic plotter which utilizes predetermined different size diameter marking instruments which are appropriately selected, with the aid of a computer, for quickly and efficiently filling in images drawn on a large sheet. This invention is particularly, though not exclusively, useful in making positives for use in screen printing, and large posters.